This invention relates generally to beam steering of coherent light and more particularly to apparatus utilizing electro-optical phase modulation of light within waveguide bundles, optical phased array emitters, electronic control circuits, and resistor grid arrays for voltage distribution.
Laser beams are used in many product applications such as laser printers, scanners, bar code readers, projectors. CD players and CD-ROM readers. Many of these devices involve the relative movement of a laser beam across a surface which is achieved by mechanical means. Typically this takes the form of movement of the laser device itself, the deflection of the beam by means of movable mirrors and/or prisms, or movement of the surface on to which the beam is projected. Historically, machines using mechanically moving parts have tended to be more expensive, less reliable and slower than solid state devices which achieve the same results without moving parts. In general terms, this invention is intended as a solid state alternative to the mechanical components currently used to control the direction of a laser beam, in devices such as scanners, laser printers, bar code readers, laser video displays, laser video projectors and potentially in new types of devices which require a controlled laser beam projection capability.
For a long time phased array radar systems which operate in the microwave range of the electromagnetic spectrum have used beams of electromagnetic radiation which are steered without movable antennae. The key elements constituting the basic operating principles of beam steering by means of a phased array of radiating antenna elements are part of the prior art and are shown in FIG. 1. Over the last two decades or so, there have been a number of inventions which have attempted to apply these operating principles to optical phased array systems. Most of these systems are based on electro-optical phase shifters in which a voltage is applied across an electro-optical waveguide to induce a phase shift proportional to the length of the waveguide and the applied voltage.
None of these inventions so far has been able to displace the current dominance of mechanical systems in commercial optical devices requiring steerable laser beams, because a number of deficiencies remain to be overcome. Deficiencies in the prior art relating to optical phased arrays are summarized as follows:
Fabrication of the components to the required tolerances is difficult because the small wavelength of light necessitates correspondingly small components. PA1 Photolithographic technology for fabricating small scale components has tended to focus on linear electro-optical arrays which can be steered only in one dimension. PA1 Fabrication of electro-optical waveguides with two dimensional emitting arrays has been difficult. PA1 The number of phase shifting elements in the array has been limited by the complexity of electrically connecting a large number of phase shifting elements to a control system, which in turn has resulted in relatively few emitting elements and hence wide beams with limited resolving power and beam intensity. PA1 In some cases, the use of a limited number of discrete control voltage levels in order to simplify the electrical controls and connections for a two dimensional array has restricted the ability to steer the beam continuously. PA1 The control systems have tended to be complex. PA1 EUGENE HECHT. Optics, 2nd Edition. 1987, Addison-Wesley, ISBN 0-201-11611-1 PA1 FERNANDO AGULLO-LOPEZ, JOSE MANUEL CABRERA, FERNANDO AGULLO-RUEDA, Electrooptics, Phenomena, Materials and Applications, 1994, Academic Press, ISBN 0-12-044512-3 PA1 L. J. GIACOLETTO (Editor), Electronics Designers' Handbook. 2nd Edition, 1977, McGraw-Hill, ISBN 0-07-023149-4 PA1 JACOB MILLMAN. CHRISTOS HALKIAS, Integrated Electronics: Analog and Digital Circuits and Systems, International Student Edition, 1972, McGraw-Hill Kogakusha, Library of Congress Catalog Card Number 79-172657 PA1 DANIEL LAPEDES (Editor), McGraw-Hill Dictionary of Scientific and Technical Terms. 2nd Edition, 1978, McGraw-Hill, ISBN 0-07-045258-X PA1 to create a waveguide bundle of phase modulator elements terminating in a two dimensional emitting array which is easier to fabricate than alternatives using traditional photolithographic techniques; PA1 to produce an output beam which can be steered independently in two separate dimensions by means of two respective input control signals; PA1 to produce an output beam which can be steered continuously over its entire operating range; PA1 to create simplified connections between the electronic control circuit and the phase modulator elements by the use of a resistor grid array and a base bias grid to distribute transverse voltages to the phase modulator elements; PA1 to create a simplified electronic control circuit to apply variable control voltages across the phase modulator elements in the array; PA1 to create a basic apparatus which easily lends itself to scaling up into a very large array; and PA1 to produce a narrow output beam from a large number of emitting elements. PA1 An existing monolithic laser scanning device contains a one dimensional emitting array which limits scanning to one dimension, whereas this invention has a two dimensional emitting array which can scan in two dimensions. PA1 Another type of phased array laser scanner which is part of the prior art uses a phase delay in the laser output between adjacent laser devices, whereas this invention uses phase modulator elements rather than the laser devices themselves to induce the phase shift in the light. PA1 Also part of the prior art is a beam control in two dimensions for an optical phased array, which is fabricated from two three-dimensional units each consisting of a number of plates stacked adjacent to one another and positioned at 90 degrees relative to one another, one unit to achieve directional control in one dimension and the other unit to achieve directional control in the perpendicular dimension. In contrast, this invention has an integrated waveguide bundle, without the need for a 90 degree transposition in the middle of the waveguide. PA1 The prior art includes a beam controlled by a series of binary reverse polarity voltage distributions. This invention on the other hand, utilizes a reference control voltage and three analog control voltages which can be continuously varied and distributed across the array in a predetermined pattern by a control and distribution circuit consisting of an electronic control circuit and a resistor grid array.
References to specific documents containing information related to this invention are as follows:
______________________________________ U.S. Pat. No. Donald R. Scifres 11/23/1982 Monolithic Laser 4,360,921 et al. Scanning Device U.S. Pat. No. David L. Fried 8/16/1988 Agile Beam Control 4,764,738 of Optical Phased Array U.S. Pat. No. George E. Hanson 7/7/1998 Phased Array 5,777,312 Laser Scanner U.S. Pat. No. Suwat Thaniyavarn 5/12/1998 Phased Array Beam 5,751,248 Controller Using Integrated Electro- Optic Circuits U.S. Pat. No. Suwat Thaniyavarn 8/6/1996 Phased Array Beam 5,543,805 Controller Using Integrated Electro- Optic Circuits U.S. Pat. No. Donald B. Keck 1/16/1973 Method of Pro- 3,711,262 et al. ducing Optical Waveguide Fibers ______________________________________
Section 18: Wave Shaping Circuits PA2 Section 26 Radar and Navigational Systems